The large scale mining of materials tends to be an energy intensive endeavor. In many opencast mines, a fleet of large mining trucks may operate almost continuously to transport ore and overburden from an extraction area to a dump or processing site. Many such mining trucks are operated via diesel-powered engines. Both direct drive diesel engines and diesel-electric drive systems have been used over the years. As with many other heavy equipment systems, fuel costs for mining trucks can be substantial. Moreover, many mines are located in remote locations, and the costs of transporting fuel to the mine site can add significantly to the operational expense. Even obtaining sufficient fuel supplies can be challenging, regardless of cost. For these and other reasons, engineers in the mining industry and mining equipment manufacturers are continually searching for ways to reduce fuel consumption. Given the historical price volatility of commodities, of which mined materials and petroleum fuels are both examples, as well as variation in geology and topography among mine sites, the economics of supplying and consuming energy for mining activities tends to be complex and variable.
For decades mine operators have experimented with the use of electric power generated on-site or supplied from a utility grid, to power mining equipment. On-site electric power generation has similar cost and availability concerns to fueling equipment directly via petroleum fuels. Due to the remoteness of many mines and other factors, supplying electrical power from a grid, even over relatively long distances, has proven consistently advantageous for at least certain mines as compared to reliance on petroleum fuels alone. Electric power costs can nevertheless vary due to market fluctuations, as well as varying from mine to mine depending upon regional availability of fossil fuels, geothermal or hydroelectric power, or other native or obtainable sources of energy for electricity generation. Thus, even where electric powering of mining equipment is viable, there remains ample motivation to use it as efficiently as possible, both to control costs and optimize predictability in the face of uncertain economics.
While first proposed decades ago, one contemporary example of the use of electric power at mine sites is a trolley system having an overhead trolley line to provide electrical power to assist mining trucks, particularly when traveling loaded upon uphill grades. Many opencast mines include a haul road extending from an extraction site for ore to a remote dump site or processing location. The mining trucks used at such site may need to travel an uphill grade on the haul road that is several kilometers long, or possibly even longer. It will be appreciated that the use of diesel or other petroleum fuels to propel mining trucks carrying literally hundreds of tons of ore up such grades can be quite costly, and thus trolley systems have received renewed interest in recent years.
Mining trucks configured to be assisted with electrical power from a trolley line typically include a mechanism known as a pantograph which can be used to reach upwardly and/or outwardly from a mining truck to electrically contact the trolley line, and thus provide electric power for propulsion rather than generating the power on-board the mining truck itself. In conventional practice, an operator visually monitors the proximity of their mining truck to an overhead trolley line, and actuates the pantograph to engage the trolley line at a desired location, then disengages the pantograph from the trolley line at its end. Mining truck operators are already tasked with steering and otherwise controlling what amounts to an extraordinarily large and heavy machine. Accordingly, highly skilled operators having extensive training and experience are often selected for operating mining trucks. Despite such skill and training, operators tend to direct their attention more to avoiding obstacles and collisions than optimally timing the actuation of the pantograph. Moreover, steering a mining truck such that it remains electrically connected with the trolley line can itself be a challenging endeavor. As a result, many mining trucks are operated less often, or more conservatively, on-trolley than they optimally might be. Adding still further to these challenges is the fact that a trolley line may not always be available. Maintenance, repairs, and electrical faults generated where trucks unintentionally steer off or onto a trolley line can require the trolley line to be temporarily de-energized, disrupting smooth and predictable flow of operations at the mine.
U.S. Pat. No. 4,694,125 to Takei et al. is directed to a collector device for trolley-assisted vehicles having a pantograph circuit. The circuit de-energizes a valve controlling pantograph position when a driver leaves the vehicle. In other words, Takei et al. appear to propose disconnecting the pantograph from a trolley line when an operator stops the truck and intends to exit. While preventing electrical shocks to an operator is surely a valid goal, Takei et al. appear to offer no solutions to the challenges of energy consumption, costs, and efficiency at modern mine sites.